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EFFECTS OF DIABETES ON CALCIUM UPTAKE BY RAT BRUSH BORDER MEMBRANE VESICLES
Author(s) -
Schedl Harold P.,
Christensen Karla K.,
Ronnenberg William C.
Publication year - 1995
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1995.tb01993.x
Subject(s) - brush , vesicle , brush border , calcium , diabetes mellitus , chemistry , biophysics , membrane , medicine , endocrinology , biology , biochemistry , materials science , composite material
SUMMARY 1. We investigated the mechanism of decreased transmucosal calcium transport in the gut of the diabetic rat by comparing calcium uptake by brush border membrane vesicles from control and streptozotocin diabetic rats at 5 days. Brush border calcium uptake consists of saturable and non‐saturable components. Saturable uptake is mediated by a specific mobile carrier mechanism and is defined by V max (saturable uptake of calcium at infinite medium calcium concentration) and K T (calcium concentration at V max /2). Non‐saturable uptake is defined by k D (rate constant for non‐saturable uptake per unit calcium concentration), and comprises both diffusive and surface binding components of calcium uptake. 2. We found both saturable and non‐saturable calcium uptake to be decreased ( P < 0.05) in diabetes. Comparing control and diabetic, V max was 247 compared to 152 (data are pmol/mg protein per 3 s); k D was 285 compared to 172 (data are pmol/mg protein per 3 s at 1 mmol/L calcium); and K T (mmol/L) did not differ between groups, 0.070 compared to 0.057. 3. The decreased V max in the setting of unchanged K t in vesicles from diabetics is consistent with decreased calcium transporter specific activity, rather than with altered transporter function. 4. Since (i) V max is decreased by vitamin D deficiency in the normal rat, and (ii) circulating 1α,25‐dihydroxycholecalciferol is decreased in the diabetic rat, decreased V max in the diabetic may be related to the low 1α,25‐dihydroxycholecalciferol. 5. Since vitamin D deficiency does not alter k D in the normal rat, the decreased k D in diabetes may be an effect of diabetes on the membrane. In conclusion, decreased transmucosal calcium transport in diabetes is, at least in part, the consequence of decreased brush border uptake.